Hard disk drives have become a dominant persistent data storage medium for computers since their introduction in the 1950's. The storage capacity of hard disk drives has steadily increased over the years while cost per unit of storage has decreased. For example, areal density of the magnetic disks has doubled every two to four years without significant increase in per-unit cost. As a result, hard disk drives continue to have advantages over competing storage technologies such as solid-state drives at least in terms of price per unit of storage.
New magnetic storage technologies are being developed to maintain this rate of areal density growth of hard disk drives. Some of these technologies include heat-assisted magnetic recording (HAMR), bit-patterned recording (BPR), shingled magnetic recording (SMR), and two-dimensional magnetic recording (TDMR). For these technologies, increased areal density will likely result in reduced track pitch, such that reading back data from the tracks becomes more challenging.